MIC5202

Micrel

3-140

July 1998

Thermal Considerations

Applications Information

External Capacitors

A 1

µF capacitor is recommended between the MIC5202

output and ground to prevent oscillations due to instability.

Larger values serve to improve the regulator's transient

response. Most types of tantalum or aluminum electrolytics

will be adequate; film types will work, but are costly and

therefore not recommended. Many aluminum electrolytics

have electrolytes that freeze at about –30

°C,sosolidtantalums

are recommended for operation below –25

°C. The important

parameters of the capacitor are an effective series resistance

of about 5

Ω or less and a resonant frequency above 500kHz.

The value of this capacitor may be increased without limit.

At lower values of output current, less output capacitance is

required for output stability. The capacitor can be reduced to

0.47

µF for current below 10mA or 0.33µF for currents below

1 mA. A 1

µF capacitor should be placed from the MIC5202

input to ground if there is more than 10 inches of wire between

the input and the AC filter capacitor or if a battery is used as

the supply.

ENABLE Input

The MIC5202 features nearly zero OFF mode current. When

the ENABLE input is held below 0.7V, all internal circuitry is

powered off. Pulling this pin high (over 2.0V) re-enables the

device and allows operation. The ENABLE pin requires a

small amount of current, typically 15

µA. While the logic

threshold is TTL/CMOS compatible, ENABLE may be pulled

as high as 30V, independent of the voltage on V

portions of the MIC5202 may be enabled separately.

General Notes

The MIC5202 will remain stable and in regulation with no load

in addition to the internal voltage divider, unlike many other

voltage regulators. This is especially important in CMOS

RAM keep-alive applications. Thermal shutdown is

independant on both halfs of the dual MIC5202, however an

over-temperature condition on one half might affect the other

because of proximity. When used in dual supply systems

where the regulator load is returned to a negative supply, the

output voltage must be diode clamped to ground.

Both MIC5202 GROUND pins must be tied to the same

ground potential. Isolation between the two halfs allows

connecting the two V

PC Board

θ

JA

Dielectric

FR4

160

°C/W

Ceramic

120

°C/W

Multi-layer boards having a ground plane, wide traces near

the pads, and large supply bus lines provide better thermal

conductivity.

The "worst case" value of 160

°C/W assumes no ground plane,

minimum trace widths, and a FR4 material board.

Part II. Nominal Power Dissipation and Die Temperature

The MIC5202-xxBM at a 25

°C ambient temperature will

operate reliably at up to 625mW power dissipation when

mounted in the "worst case" manner described above. At an

ambient temperature of 55

°C, the device may safely dissipate

440mW. These power levels are equivalent to a die tempera-

ture of 125

°C, the recommended maximum temperature for

non-military grade silicon integrated circuits.

Part I. Layout

The MIC5202-xxBM (8-pin surface mount package) has the

following thermal characteristics when mounted on a single

layer copper-clad printed circuit board.

245 mil

30 mil

50 mil

50 mil

150 mil

Minimum recommended board pad size, SO-8.